Keep writing about Russia and Eastern Europe.

Saying that China alone has the leverage to end the North Korean nuclear program is besides the point.  In fact, you may want to provide more information as to what incentives China has for really "putting the hurt on Pyongyang" because while I agree they're worried about a nuclear arms race (as opposed to the conventional one that's been going on for years) in East Asia, fear of fallout and Korean missiles isn't very compelling stuff. 

Right now, China's trying to triangulate between the U.S. and North Korea in order to protect its newly realized, less confrontational while economically lucrative relationship with the Americans yet avoiding anything that would precipitate the disorder of the Kim regime falling apart.  See they share a border with North Korea and fear the results of such a collapse would destabilize Northeastern China (historically a national achilles heel) so cutting off food and oil supplies or opening the border to hundreds of thousands of refugees is really the last thing they want to do right now regardless of how well it worked in Eastern Europe?  Trust me they've already told the North the PRC probably won't honor military alliances if they provoke a confrontation, but in general Chinese foreign policy doctrine also place a premium on non-aggression and respect for national integrity that means they really don't favor the more belligerent rhetoric coming from the likes of Ambassador Bolton either.  From what I've read I'm under the impression the Chinese hope that either the North Koreans are able to survive due to implementing needed economic and political reforms or that an orderly, negotiated reunification with the South in the near future will prevent chaos and lessen tensions in the region -- doing something that "turns off the light in Pyongyang" while impressive accomplishes neither.  Although they feel the need to be part of any ultimate solution, they're gonna dance for the time being. 

Also, while its comforting to say the U.S. government has nothing to offer and no leverage with the North that's really a dodge, Anne.  You've written books about totalitarian regimes so I shouldn't have to tell you that most totalitarian dictatorships have an overwhelming need for self-preservation and no matter what they might get into they'll look for a way out that ultimately maintains their hold on power.  North Korea's no different although if your argument is the Kim regime doesn't deserve to survive that's another matter.  Nevertheless, I'll bet you that when and if we decide to sit down with them we'll write something up that says,  "We want you to do this, this and this" and they'll look at it and say, "We like the part about you agreeing not to invade".